1. Field of the Invention
This invention relates to an optical communication device, that is, an optical transmitting device (LD, LED module), an optical receiving device (PD module) and transmitting/receiving device (LD/PD module). This invention aims at a small-sized, inexpensive optical communication device which makes the best use of the planar waveguide circuit (PLC) technology for photodiodes (PD) and laser diodes (LD) (or LED) including peripheral electronic devices.
This application claims the priority of Japanese Patent Application No.2001-61653 filed on Mar. 6, 2001 which is incorporated herein by reference.
2. Description of Related Art
FIG. 1 and FIG. 2 show the known optical communication device stored in a plastic (resin) mold type package. The resin package 1 includes a printed circuit board 2, an optical module 3, a first integrated circuit chip (IC) 4, a second integrated circuit chip (IC) 5, and R/C elements which are either resistors (R) or capacitors (C). The circuit board 2 is a planar resin board (e.g., epoxy resin) printed with wiring patterns having holes. Pins of the ICs 4 and 5 and pins of the R/C elements are inserted and fixed in the holes of the wiring patterns on the printed circuit board 2. The optical module 3 has a package, a set of pins 9 at the back and a receptacle 10 at the front. The package includes at least one optoelectronic device, that is, a photodiode (PD), a laser diode (LD) or a light emitting diode (LED).
When the optical communication device is a transmitting device, the optical module 3 includes an LD or an LED. The LD or LED is a light source which emits transmitting signal light. The IC 4 and the IC 5 are driving ICs which amplify transmitting signals and give driving current to the LD or the LED.
When the optical communication device is a receiving device, the optical module 3 includes a PD or an APD which converts light signals to electric current signals (photocurrent). The IC 4 and the IC 5 are preamplifiers which amplify the photocurrent. In FIG. 1 and 2, the device has a resin molded type package 8. Instead of the resin mold, the device is sometimes stored in a case package which is either a metallic case or a ceramic case having outer walls and an inner space. The case is hermetically sealed.
The known structure of FIG. 1 and FIG. 2 was proposed, for example, by    {circle around (1)} Japanese Patent Laying Open No.7-106608(106608/'95), “Optical Receiver”.
The optical module 3 is an independent device sealed in a metallic package in the Prior Art of FIG. 1 and FIG. 2. Ends of the pins of the module 3 are soldered to wiring patterns on the print circuit board 2. The optical module 3, the circuit board 2, and the ICs 4 and 5 are stored in the metallic package 1. The metallic package 1 has leadpins (not shown). The cylindrical receptacle 10 protrudes from the front of the optical module 3. An end of an optical fiber 11 is inserted to the receptacle 10. The optical fiber 11 connects this unit with a partner optical communication unit. In the case of the receiving device, the optical signals propagating from the partner are received by a PD in the module 3. In the case of the transmitting device, an LD injects transmitting signals in the optical fiber 11.
FIG. 3 is an enlarged sectional view of the optoelectronic module 3 in the transmitting/receiving device shown in FIG. 1 and FIG. 2. The optoelectronic module 3 is an independent device having several elements which are stored in a metallic package. A metallic disc stem 12 has a projection 15 standing on a top surface. The projection 15 supports a laser diode (LD) 13 on an inner side. The laser diode emits forward light and rear light. A photodiode 14 is mounted at the center of the stem 12 just below the LD 13 for monitoring the power of the rear-emitted LD light. A cylindrical cap 17 is fitted upon the stem 12. The cylindrical cap 17 has a ball lens 16 at a top opening for converging the light emitted forward from the LD 13. A cylindrical metallic sleeve 18 with a top opening retains the stem 12, the PD 14, the LD 13, the lens 16 and the cap 17.
The forward-emitted LD light rays are converged by the lens 16 at an end of an optical fiber 11 and are introduced into the fiber 11 as signal light. The rear-emitted LD light are irradiated to the monitoring PD 14. Lead pins 9 protrude from the bottom of the stem 12 for introducing driving current to the LD 13, for applying reverse bias to the monitoring PD 14 and for outputting monitoring signal from the PD 14. The metallic sleeve 18 and the metallic stem 12 seal the inner space hermetically.
Paring and storing the known LD module and PD module of FIGS. 1 and 2 into a package give the Prior Art of an LD/PD module which is shown in FIG. 11. A transmitting (LD) portion is constructed by soldering pins 9 of a metallic-packaged LD 3, pins of an LD driving IC 4, pins of an APC-IC 5, and pins of R/C elements 6 and 7 to wiring patterns prepared upon a first print circuit board 2. Since the printed patterns convey electric currents, the LD part dispenses with a bonding-wire. A receptacle 10 is attached to a front end of the metallic-packaged LD 3.
A receiving portion is built by soldering pins 9′ of a metallic-cased PD 3′, pins of a main amplifier IC 4′, pins of a waveform-reforming IC, pins of a timing-adjusting IC, pins of a buffer IC, and pins of R/C elements 6′ and 7′ to wiring patterns made upon a second print circuit board 2′. The printed patterns carrying currents expel bonding-wires from the PD part. A receptacle 10′ is upholstered to a front of the metallic-cased PD 3′. A large, wide package 1 encloses the PD part and the LD part arranged in parallel side by side. An optical fiber 11′ is joined to the receptacle 10′ of the PD part for taking in receiving signal light propagating in the fiber. The LD/PD module of FIG. 11 is too long, too wide and too thick. This known module is overall too large in three directions.    {circle around (2)} Susumu Nakaya, “MU interface compact 155 Mb/s 3R-optical transceiver module”, Proceedings of the 1999 Communications Society Conference of IEICE, B-10-112, p289, proposed a module having a transmitting part and a receiving part in parallel. The transmitting part consists of a receptacle, an LD and a circuit board with ICs. The receiving part consists of a receptacle, a PD and another circuit board with ICs.    {circle around (3)} M. Shishikura, T. Hirataka, K. Yoshida, K. Tatsuno, and S. Tsuji, “Plastic Mini-DIL PIN-PREAMP modules using low capacitance Si optical-bench”, Proceedings of the 1999 Communications Society Conference of IEICE General Conference, C-3-10, p164, proposed a receiving module (PD module) having an optical bench (substrate), a PD and an IC mounted on a rear half of the optical bench and an optical fiber fitted on a front half of the optical bench. The optical bench, the optical fiber, the PD and the IC are accommodated in a resin-molded package. The inner space of the plastic package is filled with resins. This is described here as an example of the Prior Art of the PLC (planar lightguide circuit) type modules.    {circle around (4)} H. Hotta, T. Nakamura, K. Naitou, T. Sakai, Y. Tashita, H. Arimoto, Z. Sekine, and M. Sudou, “Surface mount type high power LD module”, Proceedings of the 1998 IEICE General Conference, C-3-7, p173, proposed an LD module having a silicon bench, an optical fiber provided upon the silicon bench, an LD and a monitoring PD mounted upon the silicon bench and a resin-molding package enclosing the silicon bench, the LD, the PD and the fiber. This LD module lacks ICs and electronic circuits. This is cited here as another example of the Prior Art of the PLC type modules.
The transmitting/receiving module shown in FIG. 1 and FIG. 2 proposed by {circle around (1)} and {circle around (2)} stores an LD into a metallic package and a PD into another metallic package. The metallic packages have large volumes as shown in FIG. 3. The metallic packaged LD and PD are accompanied by electronic circuits (LD driving ICs, amplifier ICs and so on) furnished on epoxy resin print circuit boards. The module is long, thick and bulky. The module requires many numbers of parts. Such an LD module or a PD module is unfavorable for reducing cost and size.
The PLC has a strong point of reducing the thickness of modules, since the PLC disposes a laser diode or a photodiode on a silicon bench and attaches an optical fiber to the silicon bench for aligning the PD or the LD, which is called passive alignment. Prior Art {circle around (4)} is an example of an LD module which loads an LD on a silicon bench, aligns an optical fiber in a groove on the same silicon bench and encloses the sample into a plastic package.
Prior Art {circle around (3)} is an example of a PD module which loads a PD on a silicon bench, aligns an optical fiber in a groove on the same silicon bench and encloses the sample into a plastic package.
Prior Art {circle around (4)} and {circle around (3)} contain neither electronic elements (preamplifier IC, LD-driving IC, amplifier IC, waveform-reshaping IC, buffer IC, auto power controlling IC etc.) nor electric elements (R/C elements; namely resistor R, capacitor C, inductance L). The electronic elements and electric elements have been loaded upon an independent, separated circuit board succeeding to the optoelectronic (LD, PD, LD/PD) module as demonstrated by FIG. 1 and FIG. 2. The optoelectronic (LD, PD, LD/PD) module 3 has long leadpins 9 on the bottom. Soldering the leadpins to wiring patterns on the circuit board 2 allows the optoelectronic module electrical connection to electronic elements or electric elements on the circuit board 2.
Thus, if the metallic packaged optoelectronic (LD, PD, LD/PD) module 3 of FIGS. 1 and 2 is replaced by a PLC type optoelectronic (LD, PD, LD/PD) module, the module length is scarcely shortened. Blunt replacement of the metal packaged module by the PLC module is insignificant. Peripheral electronic or electric elements which accomplish the function of the modules should be taken into account.
Sizing down of unified modules including electronic elements is important.
One purpose of the present invention is to provide a downsized optical communication device (optoelectronic elements (LD, PD, LD/PD) and electric, electronic elements) having a short length, a small width and a thin thickness.
Another purpose of the present invention is to provide a low cost optical communication device (optoelectronic elements (LD, PD, LD/PD) and electric, electronic elements) by reducing the number of necessary parts and simplifying assembling steps.
A further purpose of the present invention is to provide a high-speed optical communication device (optoelectronic elements (LD, PD, LD/PD) and electric, electronic elements) by shortening wiring distances between optoelectronic elements and electronic elements.